In the past, it has been desirable to collect flash-spun continuous fibers from a spinneret in the form of a rod-shaped batt, commonly known as a log, wherein the fiber in the batt may be unwound from the end opposite from which the fiber was fed into the batt. This is commonly referred to as being backwindable. For example, U.S. Pat. Nos. 3,413,185; 3,417,431; and 3,600,483 all disclose processes for forming such logs. In brief, the process for forming such logs generally comprises collecting the fiber from a spinneret in a tubular shaped perforated collecting conduit. As the fiber collects therein, it takes the shape of the conduit, i.e. a rod shaped batt. The solvent, which is discharged from the spinneret with the polymer fiber, flash evaporates and expands into the conduit compressing the fiber into the log, pushing the log forward in the conduit, and escaping through the gas release ports in the periphery of the conduit.
In the foregoing references, it should be noted that the spinneret does not include a tunnel at the exit thereof. As is disclosed in U.S. Pat. No. 3,081,519 (Blades et al.) and U.S. Pat. No. 3,227,794 (Anderson et al.), a tunnel has a significant effect on fiber tenacity. U.S. Pat. No. 4,352,650 (Marshall) discusses the optimization of tunnel configuration for increasing fiber tenacity from about 4.2 gpd to about 5.2 gpd, wherein fiber tenacity is described as being increased by as much as 1.3 to 1.7 times by using an appropriately sized tunnel at the exit of the spinneret. Accordingly, it would be very desirable to use a tunnel and obtain higher tenacity fiber for the rod-shaped batts.
However, when collecting the fiber into a log, it has long been believed that the expanding jet of solvent vapor must be allowed to expand fully and quickly so as to reduce or avoid the turbulence that is created by the high speed gases downstream of the spinneret. Such turbulence tends to randomly collapse the fibers prior to the fibers being collected into the log, and the fibers become disorganized as they are collected. The fibers are thereby sufficiently entangled to render the resulting log difficult to backwind. It is much preferable for the fiber to be collected while still in the expanded state so as to form a more organized log which is far easier to backwind.
A further shortcoming of prior art logmaking methods is that quite frequently, fibers momentarily exit the gas release ports located along the fiber collection tube with the expanding gas. This condition damages the continuity of the plexifilamentary structure of the flash-spun fibers resulting in more frequent filament breaks during backwinding of the flash-spun fibers making up the log. Moreover, fibers exiting the gas release ports leave continuous marks in the form of heavy axial ribs on the surface of the resulting log. These axial ribs change the resistance of log motion through the collection tube in an unpredictable manner. Due to this condition, logs produced are not consistent in quality.
A further problem of prior art logmaking arrangements is the mechanical gate at the collection tube exit for initiating the logmaking process. The gate quite frequently catches fibers during start-up which results in start-up failures and adds to the cost of production.
Another problem with prior arrangements is the mechanical friction element such as rubber gaskets that provide resistance to the log passing out of the collection tube. Clearly, it is preferable for the logs to be discharged from the collection tube in a smooth, continuous and progressive manner. However, such mechanical devices are crude, unreliable and not adapted for adjusting or modifying the rate of discharge during operation of the collection arrangement.
Clearly, what is needed is an apparatus and method that overcome the problems and deficiencies inherent in the prior art. In particular, what is needed is a logmaking apparatus which will produce strong, highly oriented, flash-spun, continuous, backwindable fibers when formed into logs. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the attached drawings and to the detailed description of the invention which hereinafter follows.
The objects of the invention are achieved by the provision of an apparatus for collecting continuous fibers moving with a stream of relatively high speed gases into a nozzle section arranged to receive the fibers and high speed gases to gradually slow the gases and fibers prior to collection thereof in a collection tube. The nozzle section has a diverging internal contour wherein it has a diverging half angle of less than or equal to about 20 degrees and the collection tube is arranged to discharge the gases through the periphery and collect the fibers in a rod-shaped batt in the central passage thereof.